Thanks leocg, I have tried some of the advises mentioned in the web site you mentioned. But nothing seems to be working. You said it doesn't seems to be opera error but all apps can be downloaded and installed from google play except opera mini and opera mini beta. I tried many times all in vain till now. We don't have picture attachment otherwise I would have the screenshot. But I give screenshot in text as below:

Can't install app:

"Opera Mini - fast browser can't be installed". Try again and if the problem continues get help troubleshooting. (Error Code:-26)